I have a class A motor home with a Ford V10 engine in it. As long as we are travelling on level ground and holding a steady speed, it runs great. But when we come to a slight grade and I have to push on the throttle, it beguins to buck and act like it is going to shut down. The check engine light is on. I replaced the fuel filter but that did no good. Fuel pump was changed out three years ago. Any ideas what the problem could be. Stuart